The invention relates to a silver-based contact material for switchgear used in power engineering, in particular for contact pieces in low-voltage switchgear which, besides silver, contains at least iron oxide and zirconium oxide as active components.
Contact materials of the system silver-metal (AgMe), on one hand, and of the system silver-metal oxide (AgMeO), on the other hand, are known for contact pieces in low-voltage switchgear used in power engineering, for example in power circuit-breakers as well as in d.c. contactors and contactor relays. Representatives of the first system are, for example, silver-nickel (AgNi) or silver-iron (AgFe); representatives of the second system are, in particular, silver-cadmium oxide (AgCdO) or silver-tin oxide (AgSnO.sub.2). Other metal oxides such as, in particular, bismuth oxide (Bi.sub.2 O.sub.3), copper oxide (CuO) and/or tantalum oxide (Ta.sub.2 O.sub.5) can be added to the latter.
The practical usability of a contact material based on silver-metal or silver-metal oxide is determined by the so-called electrical properties spectrum of the contact. Determining characteristics in this connection are, on one hand, the number of operations in a lifetime which is determined by the erosion of the contact member, and, on the other hand, by the so-called excess temperature, i.e. the heating of a contact bridge which results essentially from the electrical resistance of the contact constitution named. In addition, a sufficiently slight welding tendency of the contact pieces and, furthermore, a resistance to corrosion are important since, especially due to long-term corrosion of the material in air-break switchgear, the switching properties can change with time.
From the German laid open print 41 17 311, a contact material is known of the type named at the outset in which iron oxide in percentages by mass between 1 and 50% and an oxide of a further chemical element in percentages by mass between 0.01 and 5% are present in combination as active components. In that case, zirconium oxide, i.a., is named as the further metal oxide. The combination in particular of iron oxide and zirconium oxide has proven to have a favorable spectrum of switching properties.
In many application cases, the latter new material can advantageously replace silver-nickel materials which have been used till now and which in increasing measure are regarded as toxic because of the nickel dust produced during manufacturing and its damaging effects on the human organism. A material especially of the constitution AgFe.sub.2 O.sub.3 /Fe.sub.3 O.sub.4 ZrO.sub.2, besides being distinguished by low contact heating, stable heating behavior, negligible tendency to weld and long lifetime, is also distinguished in particular by good resistance to corrosion.